The present invention relates in general to a mechanical, demand-type, paper sheet feeder for feeding pre-cut sheets of paper or envelopes from different paper trays a rotating printer platen. More specifically, the paper sheet feeder includes various feed rollers associated with the different paper trays, and which are adapted to be forwardly driven for paper sheet feeding by rotation of the printer platen in a forward paper introduction direction, with selection of the appropriate paper tray from which sheets of paper or envelopes are to be fed being made by a combination of forward and reverse rotations of the printer platen. In this regard, once the appropriate paper tray has been selected by the appropriate combination of reverse and forward rotations of the printer platen, the corresponding feed rollers are rotated only by forward rotation of the printer platen for introducing sheets of paper or envelopes into the printer.
Tremendous advances have been made in the last few years in automating office procedures. Conventional typewriters have grown into mini-computers for performing word processing, storage and other functions. The speed at which these machines produce words on paper is increasing at a rapid rate. As added speed and sophistication are developed into such machines, the actual putting of words onto paper becomes ancillary to the main function of collecting and organizing the information into a format to be printed. In order to have flexibility and speed, many systems have been developed where an operator manipulates words on a cathode ray tube or other word processing equipment until the final copy is in the format desired. With all of these advantages, it has developed that today one of the major bottlenecks in terms of time, and therefore usefulness of this equipment, is the rate at which paper can be brought to and move past a printing head to produce the final hard copy.
Of course, it is possible to use continuous sheets of perforated paper, as is commonly done in computer applications, having sprocket holes along the sides thereof to continuously feed and move the paper through an impact printer. This, however, requires special paper which is not suitable to the many requirements for which normal typewriting is employed.
Many machines exist, both copying machines and printing machines, which automatically feed paper past a printing or reproducing station. These machines are normally run synchronously such that prior to the time the paper is fed, the information to be printed on the paper is already organized and the papers move past the printing head in a continuous fashion. This is not generally suitable for impact printing devices, since impact printing is accomplished with the paper stationary rather than moving, and further the adaption of normal typewriting type printing requires moving of paper not only in an intermittent basis, but also in the forward and reverse direction in accordance with the information to be typed. Still further, with such existing equipment, it is generally not possible to manually feed separate sheets of paper, which may be of different size or thickness such as, for example, envelopes, without disconnecting the equipment from the printing machine.
In U.S. Pat. No. 4,326,815, which patent is assigned to the same assignee of the present invention, there is disclosed a paper sheet feeding apparatus, including a removable paper tray, which is capable of being retrofitted with respect to existing printing devices, i.e., distributed as an after market product, as well as being capable of being sold and distributed with the printing device. The retrofit characteristic of this paper sheet feeding apparatus lends itself to conform to the climate of the existing impact printing devices, rather than requiring the radical modification thereof, so as to conform with the needs of high speed paper feeding. Another known paper feeding apparatus adapted to be retrofitted onto an existing printing device is known from U.S. Pat. No. 4,248,415. Although the former known paper sheet feeding apparatus has been commercially successful, the selection of a paper tray is software dependent upon a stored program routine. This necessitates the use of a microprocessor and suitable hardware responsive to the specially designed program. On the other hand, although the latter known paper sheet feeding apparatus is of the mechanical type, such apparatus requires the use of a mechanical assembly which may prove unreliable over extended use.